The current method of providing cable TV signals to a house requires that a cable branch (typically a coaxial cable) connect from the main cable trunk to each subscriber. In addition, at the end of the subscriber branch, an additional segment of the coaxial cable must be installed for every extra TV "hookup" within the residence.
The challenge of providing cable TV to an apartment building is even more formidable. If coaxial cabling is not included at the time of construction, a coaxial cable leading through the entire building must be installed, and a branch must connect between each of the individual apartment units to a point on this cable. This is obviously an expensive procedure, even if easily accessible cabling conduits exist. Furthermore, each branch provides service at only one location within the unit it connects. Extra branches must be installed to provide cable TV service at other locations in the unit.
Providing a group of TV signals to various rooms in an office building currently requires a similar amount of coaxial cable installation. The demand for economical video distribution within office buildings is increasing, moreover, because of the increased popularity of video teleconferencing.
The method of distributing cable TV signals commonly used in the U.S. can be called a "one-way branched" system because signals transmitted at the head-end (i.e., at the root or entrance point to the network) spread across to each of the various subscribers by continually splitting into multiple downstream branches. Due to an increase in the popularity of video programming, however, demand for a new system has emerged. Under the new system, sometimes called "video on demand," a subscriber can request a specific program from a library of programs stored at a central location on, for example, video tapes. The signal from this program is subsequently sent to the subscriber from the "head end" of the system. No other viewers can receive the same signal unless they make a similar request.
One method for providing video on demand is to install a high-capacity fiber optic transmission line from the library through a series of residential or commercial neighborhoods. At each neighborhood, all signals targeted for the local residences or businesses (hereinafter, the term "residence" is used to mean both types of buildings unless otherwise stated) are encoded (i.e. scrambled) and then "handed off" at different channels onto the coaxial cable branch that feeds those residences. Thus, each neighborhood has its own individual headend at the point of handoff.
To prevent all residences from receiving each of the signals handed off to their neighborhood, a control signal is sent over the fiber optic transmission line that includes the "address" of a converter box in the house of the subscriber who requests a particular signal. This control signal provides descrambling instructions that, because of the addressing, only the targeted converter box will recognize. Under this system, each subscriber receives all signals targeted for his or her neighborhood, but only the program (i.e., the specific video signal) actually requested by a subscriber becomes available to him or her in unscrambled form.
The concept of "video on demand" can be considered to be part of a broader communication concept. The broader concept is the widening of communication paths to the ordinary subscribers on the switched public communication network. This would enable subscribers to communicate video signals and other relatively wide bandwidth signals in the same way that they currently communicate voice signals.
The transmission medium that is best suited to provide wider communication paths is fiber optic cables. Indeed, many of the public telephone companies have converted most of their main communication trunks to fiber optics, and have upgraded their switching equipment to handle these signals and their attendant increase in data rates.
To bring the wider capacity to an individual site, however, requires one to install a new fiber optic branch from the main fiber optic trunk to each local network (i.e. a house, apartment unit, or a room in an office building), and to switch signals from the trunk onto the branches. Furthermore, conversion from light to electrical signals must take place at the point where the branch reaches the targeted residence. (Conversion is necessary because the communication devices currently found in typical residences and offices respond to electrical signals.) Finally, the electrical signals must be distributed through the house.